Hi，chuangde:

 

Let’s read the code together:

 

 packet-udp.c:

decode_udp_ports(tvbuff_t *tvb, int offset, packet_info *pinfo,

         proto_tree *tree, int uh_sport, int uh_dport, int uh_ulen)

{

/*First, try to dissector udp data by udp-port*/

  if (low_port != 0 &&

      dissector_try_port(udp_dissector_table, low_port, next_tvb, pinfo, tree))

    return;

  if (high_port != 0 &&

      dissector_try_port(udp_dissector_table, high_port, next_tvb, pinfo, tree))

    return;

 

/*then ,we try heuristic subdissector table,SIP is in the heuristic dissector list of udp, so we have a try */

  if (!try_heuristic_first) {

    /* do lookup with the heuristic subdissector table */

    if (dissector_try_heuristic(heur_subdissector_list, next_tvb, pinfo, tree))

      return;

  }

/* give up finally, data handle*/

  call_dissector(data_handle,next_tvb, pinfo, tree);

}

 

packet-sip.c: 

void proto_reg_handoff_sip(void)

{

/*register udp-sip port*/

dissector_add("udp.port", UDP_PORT_SIP, sip_handle);

 

/* Add a sub-dissector to a heuristic dissector list of udp */

heur_dissector_add("udp", dissect_sip_heur, proto_sip);

 

}

 

 

Good luck

Bright

 

 

 

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